Forming method

ABSTRACT

A method of shear forming a component comprises the steps of:
         (i) providing a pre-formed metallic sheet blank, the sheet blank having a first surface and an opposite second surface, the perpendicular separation between the first surface and the second surface defining a thickness of the sheet blank;   (ii) applying a surface modification process to the first surface of the sheet blank to reduce a surface roughness of the first surface to a first predetermined roughness value;   (iii) positioning the second surface of the sheet blank against a mandrel; and   (iv) applying a roller to the first surface of the sheet blank in a shear forming operation to form the sheet blank into the component.

CROSS-REFERENCE RELATED APPLICATIONS

This disclosure claims the benefit of UK Patent Application No. GB 1702463.9, filed on 15 Feb. 2017, which is hereby incorporated herein in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates to a method of shear forming and particularly, but not exclusively, to a method of shear forming components for a gas turbine engine.

BACKGROUND OF THE DISCLOSURE

Shear forming has been used to produce conical parts from sheet and plate material for many years. Shear forming is a cold forming technology whereby a flat metal plate blank (or ‘pre-form’) is mounted onto a rotating mandrel (typically having a conical surface profile) and the material is made to flow against and up the mandrel by the action of one or more rollers. The final wall thickness is achieved by controlling the gap between the roller and the mandrel so the material is displaced axially, and generally parallel to the axis of rotation.

Sheet material used for shear forming, and having a thickness in excess of 3 mm is generally produced by a hot rolling process. When carrying out shear forming using hot rolled sheet material in its ‘as-rolled’ form, it has been observed that there is a marked reduction in fatigue properties of the material after shear forming. In addition the thickness tolerance on hot rolled sheet is often large (i.e. +/−10% from nominal values) due to process capability. This means that it is common practice for the ‘as-rolled’ sheet to be ground on both sides to meet the tolerances required by the engine application.

When used in a shear forming process, this ‘fully ground’ sheet material results in a fatigue improvement in line with established understanding. This has led to a situation whereby grinding on both sides of the sheet is often stipulated prior to shear forming, which substantially increases the cost of the shear forming process.

SUMMARY OF DISCLOSURE

According to a first aspect of the present disclosure there is provided a method of shear forming a component from a pre-formed metallic sheet blank, the sheet blank having a first surface and an opposite second surface, the perpendicular separation between the first surface and the second surface defining a thickness of the sheet blank, the method comprising the steps of:

-   -   (i) providing the metallic sheet blank;     -   (ii) applying a surface modification process to the first         surface of the sheet blank to reduce a surface roughness of the         first surface to a first predetermined roughness value;     -   (iii) positioning the second surface of the sheet blank against         a mandrel; and     -   (iv) applying a roller to the first surface of the sheet blank         in a shear forming operation to form the sheet blank into the         component.

According to the method of the disclosure, if the material blank is placed in the shear forming machinery with the modified surface of the sheet facing towards the roller, as opposed to facing onto the mandrel, then the fatigue properties of the shear formed article do not reduce over those of the material itself.

Indeed the fatigue properties of the shear formed article are improved in line with the cold work performed on the material during the shear forming process. This is an unexpected result.

Optionally, the metallic sheet blank is formed by a rolling process, and step (ii) comprises the step of:

-   -   (ii)′ applying a surface modification process to the first         surface of the sheet blank to reduce a surface roughness of the         first surface to a first predetermined roughness value, the         second surface of the sheet blank remaining in an as-rolled         condition.

According to the method of the disclosure, if the material blank is placed in the shear forming machinery with the ‘as-rolled’ (sometimes referred to as “hot rolled”) sheet surface facing onto the mandrel, as opposed to facing onto the roller, then the fatigue properties of the shear formed article do not reduce over those of the material itself.

Optionally, step (ii) comprises the step of:

-   -   (ii)″ applying a surface modification process to the first         surface of the sheet blank to reduce a surface roughness of the         first surface to a first predetermined roughness value, and         applying a surface modification process to the second surface of         the sheet blank to reduce a surface roughness of the second         surface to a second predetermined roughness value, the second         predetermined roughness value being greater than the first         predetermined roughness value.

In another embodiment, a surface modification is applied to each of the first surface and the second surface. The roughness of the first surface is reduced to a first predetermined roughness value. The roughness of the second surface is reduced to a second predetermined roughness value. A feature of this embodiment is that the second predetermined roughness value being greater than the first predetermined roughness value.

Optionally, the surface modification process is selected from the group consisting of abrasive grinding, electrochemical grinding, electrolytic etching, electro-polishing, shot blasting, grit blasting, acid pickling, molten salt bath treatment, and etching.

Any surface modification process that substantially improves the surface finish of the first surface of the sheet blank may be used. In one arrangement, this surface modification takes the form of surface grinding. In other arrangements, the surface modification process may be electro-polishing, etching or some other equivalent technique.

Optionally, the sheet blank is formed from a material selected from the group comprising titanium alloys nickel-cobalt-based superalloys, stainless steels, and aluminium alloys.

In one arrangement, the sheet blank is formed from a 6-4 titanium alloy material.

Optionally, the first surface of the sheet blank has a first predetermined roughness value (Ra) of less than 3.0 μm.

Providing the first surface of the sheet blank with a first predetermined roughness value (Ra) of less than 3.0 μm prior to the shear forming process enables the method of the present disclosure.

Optionally, the first surface of the sheet blank has a first predetermined roughness value (Ra) of less than 2.0 μm.

Optionally, the first surface of the sheet blank has a first predetermined roughness value (Ra) of less than 1.0 μm.

According to a second aspect of the present disclosure there is provided a computer program that, when read by a computer, causes performance of the method according to the first aspect.

The shear forming apparatus may be controlled by a computer that is programmed by way of a corresponding computer program to carry out the method of the disclosure.

According to a third aspect of the present disclosure there is provided a non-transitory computer readable storage medium comprising computer readable instructions that, when read by a computer, causes performance of the method according to the first aspect.

The computer program that causes operation of the shear forming process may be stored within the computer or in a separate storage medium.

According to a fourth aspect of the present disclosure there is provided a signal comprising computer readable instructions that, when read by a computer, causes performance of the method according to the first aspect.

In an alternative arrangement, a signal may be provided to the computer that causes performance of the method of the present disclosure.

Other aspects of the disclosure provide devices, methods and systems which include and/or implement some or all of the actions described herein. The illustrative aspects of the disclosure are designed to solve one or more of the problems herein described and/or one or more other problems not discussed.

BRIEF DESCRIPTION OF THE DRAWINGS

There now follows a description of an embodiment of the disclosure, by way of non-limiting example, with reference being made to the accompanying drawings in which:

FIG. 1 shows a schematic view of a shear forming apparatus for carrying out the method of the present disclosure, with the material blank held against the mandrel;

FIG. 2 shows the shear forming apparatus of FIG. 1 with the method of the present disclosure underway; and

FIG. 3 shows schematically the fatigue performance of shear formed articles formed by the method of the present disclosure together with articles formed by the method of the prior art.

It is noted that the drawings may not be to scale. The drawings are intended to depict only typical aspects of the disclosure, and therefore should not be considered as limiting the scope of the disclosure. In the drawings, like numbering represents like elements between the drawings.

DETAILED DESCRIPTION

Referring to FIGS. 1 and 2, a shear forming apparatus that is capable of carrying out the method of the present disclosure is designated generally by the reference numeral 100.

The shear forming apparatus 100 comprises a mandrel 110 that can be rotated in a direction of rotation 112 by means of a rotary actuator 114. The mandrel 110 has a generally radially outwardly facing surface 118. This radially outwardly facing surface 118 is formed as an inverse of the desired surface profile of the finished article resulting from the shear forming process.

A pre-formed metallic sheet blank 120 is clamped against the distal end of the mandrel 110 by a clamping force 150. In this way the rotation 112 of the mandrel is transmitted to the sheet blank 120 that rotates co-operatively with the mandrel 110.

The sheet blank 120 is provided with a first surface 122 and an opposite second surface 124. In the present disclosure, the first surface 122 is subjected to a surface modification process prior to being clamped in position in the shear forming apparatus 100.

In one arrangement, the surface modification process is a surface grinding process. The surface grinding process serves two main purposes. Firstly, it enables a thickness 126 of the sheet blank 120 to be maintained to a pre-determined value. Secondly, it enables the surface roughness of the first surface 122 to be reduced to a first predetermined roughness value that is less than the surface roughness of the ‘as-rolled’ surface.

In this embodiment, the surface roughness of the first surface 122 is reduced to a first predetermined roughness value of approximately 2.0 μm. The surface roughness of the second surface is left in the ‘as-rolled’ condition.

In other embodiments, the surface roughness of the second surface may also be subjected to a surface modification process to reduce a surface roughness of the second surface to a second predetermined roughness value, with the second predetermined roughness value being greater than the first predetermined roughness value. A controllable roller assembly 140 is provided to flow form the material of the sheet blank 120 against the radially outwardly facing surface 118 of the mandrel 110.

FIG. 1 shows the sheet blank 120 clamped against the mandrel 110 before the roller assembly 140 has started the flow forming of the sheet blank 120. FIG. 2 shows the shear forming process underway. The sheet blank 120 remains clamped against the mandrel 110 by the clamping force 150. The roller assembly 140 is part way through the process of flow forming the material of the sheet blank 120 against the radially outwardly facing surface 118 of the mandrel 110.

The shear forming process continues with the roller assembly 140 flow forming the sheet blank 120 against the radially outwardly facing surface 118 of the mandrel 110 until the component is fully formed.

In the embodiment of the present disclosure, the shear forming apparatus 100 is controlled by a computer 160. The computer 160 is provided with a computer program 162 that causes the computer 160 to control the shear forming apparatus 100 to carry out the method of the present disclosure. A computer readable storage medium 164 is provided that sends a signal 166 to the computer that causes the computer 160 to carry out the claimed method.

The technology of shear forming is well known to a skilled person and the control of the shear forming apparatus 100 is not herein discussed in further detail.

FIG. 3 illustrates schematically the fatigue performance of some examples of shear forming the same component but starting from sheet blanks 120 with different combinations of surface finish on opposing surfaces.

Sheet blanks 120 having three combinations of surface finish on opposing surfaces were used. Firstly, sheet blanks 120 having both surfaces finished by grinding. Secondly, sheet blanks 120 having one surface finished by grinding, with the ground surface clamped against the mandrel and the roller assembly 140 pressed against the ‘as-rolled’ surface. Thirdly, sheet blanks 120 having one surface finished by grinding, with the ‘as-rolled’ surface clamped against the mandrel and the roller assembly 140 pressed against the ground surface.

Although in production there are no controls over which surface is placed against the mandrel an intuitive situation would be to place the smoother ground side against the smooth surface of the mandrel with the roller assembly being pressed against the ‘as-rolled’ surface. This arrangement would also give rise to the cosmetic benefit of improving the rougher ‘as-rolled’ finish during the shear forming process as a result of the action of rollers. However, in reality this arrangement results in a decrease in fatigue performance. It is postulated that this decrease in fatigue performance is caused by the rollers interacting with the rough ‘as-rolled surface’ to produce microstructural features from which fatigue initiates more readily.

As shown in FIG. 3 placing the ‘as-rolled’ surface of the sheet blank against the mandrel, with the roller assembly pressing against the ground surface of the sheet blank, results in an increase in the fatigue performance of the formed component.

Various example embodiments of the invention are described herein. Reference is made to these examples in a non-limiting sense. They are provided to illustrate more broadly applicable aspects of the invention. Various changes may be made to the invention described and equivalents may be substituted without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation, material, composition of matter, process, process act(s) or step(s) to the objective(s), spirit or scope of the present invention. Further, as will be appreciated by those with skill in the art that each of the individual variations described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present inventions. All such modifications are intended to be within the scope of claims associated with this disclosure.

Example aspects of the invention, together with details regarding material selection and manufacture have been set forth above. As for other details of the present invention, these may be appreciated in connection with the above-referenced patents and publications as well as generally known or appreciated by those with skill in the art. The same may hold true with respect to method-based aspects of the invention in terms of additional acts as commonly or logically employed.

The breadth of the present invention is not to be limited to the examples provided and/or the subject specification, but rather only by the scope of claim language associated with this disclosure. 

What is claimed is:
 1. A method of shear forming a component from a pre-formed metallic sheet blank, the sheet blank having a first surface and an opposite second surface, the perpendicular separation between the first surface and the second surface defining a thickness of the sheet blank, the method comprising the steps of: (i) providing the metallic sheet blank; (ii) applying a surface modification process to the first surface of the sheet blank to reduce a surface roughness of the first surface to a first predetermined roughness value; (iii) positioning the second surface of the sheet blank against a mandrel; and (iv) applying a roller to the first surface of the sheet blank in a shear forming operation to form the sheet blank into the component.
 2. The method as claimed in claim 1, wherein the metallic sheet blank is formed by a rolling process, and step (ii) comprises the step of: (ii)′ applying a surface modification process to the first surface of the sheet blank to reduce a surface roughness of the first surface to a first predetermined roughness value, the second surface of the sheet blank remaining in an as-rolled condition.
 3. The method as claimed in claim 1, wherein step (ii) comprises the step of: (ii)″ applying a surface modification process to the first surface of the sheet blank to reduce a surface roughness of the first surface to a first predetermined roughness value, and applying a surface modification process to the second surface of the sheet blank to reduce a surface roughness of the second surface to a second predetermined roughness value, the second predetermined roughness value being greater than the first predetermined roughness value.
 4. The method as claimed in claim 1, wherein the surface modification process is selected from the group consisting of abrasive grinding, electrochemical grinding, electrolytic etching, electro-polishing, shot blasting, grit blasting, acid pickling, molten salt bath treatment, and etching.
 5. The method as claimed in claim 1, wherein the sheet blank is formed from a material selected from the group comprising titanium alloys nickel-cobalt-based superalloys, stainless steels, and aluminium alloys.
 6. The method as claimed in claim 1, wherein the first surface of the sheet blank has a first predetermined roughness value (Ra) of less than 3.0 μm.
 7. The method as claimed in claim 6, wherein the first surface of the sheet blank has a first predetermined roughness value (Ra) of less than 2.0 μm.
 8. The method as claimed in claim 6, wherein the first surface of the sheet blank has a first predetermined roughness value (Ra) of less than 1.0 μm.
 9. A computer program that, when read by a computer, causes performance of the method as claimed in claim
 1. 10. A non-transitory computer readable storage medium comprising computer readable instructions that, when read by a computer, causes performance of the method as claimed in claim
 1. 11. A signal comprising computer readable instructions that, when read by a computer, causes performance of the method as claimed in claim
 1. 